Signal generator



April 25, 1961 R. G. PIETY ETAL SIGNAL GENERATOR Filed Nov. i6, 1955 5 Sheets-Sheet 1 HMMMQMW ATTORNEYS 5 Sheets-Sheet 2 VVVV olm

Pimm NNNL..

R.- G. PlETY ET AL SIGNAL GENERATOR w1 n mm2 25.5

R. SYJ.l Y RTN E MEE N Nmw. mem Iwan MRM w. A s. R. Y B .N @Px .I I [mm H E mm. 5 @E um?? o. o vm.

LIX N9 April 25, 1961 Filed Nov. 16, 1955 vmobmzmo April 25, 1961 R. G. PIETY ET AL SIGNAL GENERATOR 5 Sheets-Sheet .'5

Filed Nov. 16, 1955 AIAA r mwN H NNN A..

HMM# lm? ATTORNEYS April 25, 1961 R. G. PIETY ErAL SIGNAL GENERATOR 5 Sheets-Sheet 4 Filed Nov. 16, 1955 April 25, 1961 R. G. Pix-:TY ETAL SIGNAL GENERATOR 5 Sheets-Sheet 5 Filed Nov. 16, 1955 v ,of cathodes.

2,981,358 SIGNAL GENERATOR fates ate" Raymond G. Piety, Bartlesville, Okla., and Ross S. Marsden, Jr., Idaho Falls, Idaho, assignors to Phillips Petroleum Company, a corporation of Delaware riled Nov. 16, 195s, ser. No. 547,189

7 claims. (c1. 181-5) This invention relates to apparatus for generating electrical signals which vary in amplitude with respect to time in a predetermined manner. In another aspect it relates to apparatus to control the gain of seismic amplifiers.

In geophysical prospecting valuable information can often be obtained concerning subsurface formations, by means of seismic surveys. A pluralityof vibration responsive devices are positioned at or near the surface of the earth in a predetermined geometric array and an explosive charge is detonated at a region spaced therefrom. Vibratio'ns emitted from the explosive travel downwardly into the earth and are refiectedrfrorn various formaltions back to the vibration responsive elements. These vibration responsive elements generate electrical signals which are representative of the vibrations incident thereon. The signals are amplified and applied to a recording instrument. By observing the times of arrival of reflections at the various seismometers it is possible to obtain information regarding the depth and dip of subsurface formations.

sulting output signal can be employed to vary the gain of a seismic amplifier.

Accordingly, it is an object of this invention to provide apparatus togenerate electrical signals which vary in amplitude with respect to time in a predetermined manner.

Another object is to provide apparatus to control the gain of amplifiers as a function of time.

Other objects, advantages and features of the invention should become apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

Figure l is a block diagram of a first embodiment of the apparatus of this invention;

Figure 2 is a schematiccircuit diagram of a portion of the apparatus of Figure l;

Figure 3 is a schematic circuit diagram of a second portion of the apparatus of Figure l;

Figure 4 is a block diagram of a seco'nd embodiment of the apparatus of this invention; and

Figure 5 is a schematic circuit `diagram of a portion of the apparatus of Figure 4.

Referringnow to the drawing in detail and to Figure l in particular, there is shown a detonator 11 which can be employed to ignite an explosive charge to generate seismic waves. Detonator 11 also generates an electrical pulse which is applied to an input amplifier 12. The output of amplifier 12 is connected to the input of a pulse genera- In making records of this type it is often necessary to o'f the amplifier. However, if such an average gain cony trol is applied to the first stages of the amplifier the gain is often controlled by low frequencies which are not produced by reflections and are later removed by filtering. l`his produces undesired fluctuations in the gain. If filters areplaced before the automatic'gain control to rcmove these low frequencies, the signal amplitude may become so large that it is difiicult to design an input stage.

and filter which do not overload. This diliculty can be V.overcome by using a programmed gain control in which the gain of the amplifier is varied as a function of time. Y

However, programmed gain controls employed heretofore have been decidedly limited in the manner by whichl the gain can be regulated. These control systems generally have been able to increasethe gain only exponentially with respect to time.

In accordance with the present invention there is provided a -novel function generator which is capable of providing a signal which varies in amplitude with respect to time' in any desired manner. This is accomplished by using one or more glow transfer tubes having a plurality These tubes are designed so thatthedischarge can be moved progressively from one cathode to another. This movement is controlled -by energizing the glow tube `from a pulse generator of predetermined fr e- 'que nc y.V A potentiometer is .connectedto each cathode in fthe glo'w tube.- VThe settings of these potentiometers are -a'djusted Ein; accordanec withvthe desired sequential am- .plitudes of the output vsignal.A In this manner a signal is yprovidedl which varresm amplitude in thermanner corre- .incudine tothe .stringent-the rotentiemeters; The' te;

tor switch 13 which actuates a pulse generator 14. The output ofvpulse generator 14 is connected to the input of a pulse shaper 15 which provides a signal to transfer the discharge between adjacent cathodes of first and second glow transfer tubes -17 and 18. Glow tubes 17 and 18 are controlled by a glow tube switch 19 which regulates the plate voltage on the two tubes so that only one is active at a given time. The last cathode of glow tube 17 transmits a signal to a delay amplifier 20 which actuates a monostable multivibrator 21 to energize the rst cathode of the second glow tube 18. The output signals from glow tubes 17 and 1S are applied to the input of an isolation amplifier 22. The output of amplifier 22 is applied through an interpolation filter 23 and an output amplifier v24% to control the gain of a seismic amplifier 25 the latter receiving the output signal from a seis'morneter 26.

The apparatus o'f Figurerl is illustrated in detail in Figures'Z'and 3. First and second resistors 3i) and 31 are connected in series between a positive potential terminal 32 and ground. A normally closed switch 33 is connected between ground and the junction between resistors 30v and resistor 35. A normally openswitch is connected in parallel with potentiometer V36. TheY contactor of potentiometerr 36 is connected to' the control grid of Va triode 40 of amplifier 12. The cathode ofl triode 40 is connected to ground through a resistor 41 whichr is shunt- Y ed by a capacitor 42. fiheanode'of triode 4i) is connected to a positive potential terminal 43 through resistors 44 and 45. A capacitor 46 is connected between ground Yand the junction between resistors 44 and 45. The anode of triode 40 is also connected'through a capacitor-.48m

the control grid of artriode 49.v The control grid of `triode 49 is connected to -ground through Qa resistorStl.

The cathode of triode 49 is connected to ground through V a resistor 51 which is vshunted by a capacitor 52.' The ano'de of triode 4 9 is connected to? term1n"xal.,43 through esistors v54vand 4,5., Y

. AResi storsf and 5'7 are connected in series betweenv a ,Positiva rtwtial terminal Si andermaal' ,A #muur open switch 60 is connected in parallel with resistor 57. The junction between resistors 56 and 57 is connected through a capacitor 61 to the control grid of triode 49.

` The'anode of triode 49 is connected througha capacitor 62 to the control grid of a thyratron 63. The control grid ofthyratron 63 is connected to ground'thro'ugh series connected `resistors '64 'and '65. The junctionV between resistors 64 and 65 is connected to a negative potential terminal 66 through a resistor 67. The cathode and a suppressor grid of thyratron 63 are connected directly to ground. The anode of thyratron 63 is connected to a positive potential terminal 68 through `a resistor 70 and to ground through a resistor 71 and a capacitor 72.

The anode of thyratron 63 is connected through a capacitor 73 and a resistor 74 to the control grid of a triode 75 o'f pulse generator switch 13. The control grid of triode 7S is connected to ground through a resistor 76. The anode of triode 75 is connected to a positive potential terminal 77 through resistors 78 and 79. l The anode of triode 75 is also' connected to the control grid of a triode 80 through a resistor 81. The control grid of triode 80 is connected to ground through a resistor 82. The cathode of triodes 75 and 80 are connected to one another and to ground through a resistor 84 which is shunted by a capacitor 85. The anode of triode 80 is connected to terminal '77 through resistors 86 and 79. The junction between these two resistors is connected to ground through a capacitor 87. The control grid of triode 75 is connected through a resistor 88 to the anode of triode 80.

The anode of triode '80 is connected through a resistor 90 to the anode of a triode 91 of pulse generator 14. The cathode of triode 91 is connected to ground through a resistor 92. The control grid of triode 91 is connected to ground through a resistor 93 and to the anode of a triode 94 through a capacitor 95. The anode of triode 91 is connected to the control grid o'f triode 94 through a resistor 96. The control grid of triode 94 is connected to ground through a resistor 97. The cathode of triode 94 is connected to ground through resistors 98, 99 and 100 which are shunted by a. capacitor 101. The anode of triode 94 is connected to a positive potential terminal 102 through resistors 103 and 104. The junction between these resistors is connected to ground through a capacitor S.

The anode of triode 91 is connected through a resistor 119 and a capacitor 106 to the control grid` of a triode 107 of pulse Shaper 15. The junctionbetween resistor 119 and capacitor 106 is connected to ground through a resistor 108 which is shunted by a lcapacitor 109. The control grid of triode V107 is connected to ground through a resistor 110' and to a positive potential terminal 111 through resistors `112 and 113. The Ajunction between these resistors is connected to ground through a capacitor 114. The cathode of triode `107 is connected to the cathode of a triode 115 and to ground through a resistor 116. The anode of triodev107 is Aconnected to potential terminalA 111 throughV resistors 117 and 113. The anode of triode 107 is also connected through a capacitor 11S to the control grid of triode 115. The anode lof triode 115 `is connected toterminal 111 through resistors 1120 and 113. Theanodes of .triodes `107 and 115 are connected through respective capacitors 122 and 123 tol respective electrodes 124 and `125 of glow transfer tube `17.H These electrodes serve to transfer the discharge between `adjacent cathodes to a common-anode.

-nected to'ground through respective resistors 126 and 127. positive` potential terminal 130 sconnected through "a capacitor-.131 and resistors `152and 1.33 to ground.` A normally open switch '134.is connected in parallel vwith capacitor. 13:1.` The junction between `resistors (132 and 133 is connected through a` rectifier" 135 anda capacitor- 136 to the junction between resistors 119 *and108l l This Electrodes 124 and `125 are conin a circle.

apparatus Aprovides manual stepping of the glow discharge in the manner described hereinafter.

Glow transfer tube 17 can be type GSlOC manufactured by Atomic Instrument Company of Cambridge, Massachusetts. These tubes have l0 cathodes arranged A discharge can exist between any one of the cathodes and the single anode. Guide electrodes 124 and 125 permit input pulses to transfer the glow from one cathode to an adjacent cathode. The glow transfers from the last cathode back to the first and continuesaround the circle. The ten cathodes of tube 17 are connected to ground through respective potentiometers 141-150. Electrodes 124 and 125 are connected to corresponding electrodes 151 and 152 in the second glow transfer tube 18. The ten cathodes of the second tube are connected to ground through respective potentiometers 161470.

The first cathode of tube 17 is connected through a capacitor 171 to the` junction between resistors 172 and 173. The second terminal of resistors 173 is connected to ground and the second terminal of resistor 172 `is connected through a resistor 174 to a positive potential terminal 175. The junction between resistors 172 and 174 is connected through a capacitor 176 to ground. A normally closed switch 177 `is connected in parallel with resistor 173. The junction between resistors 172 and 173 is connected through a capacitor 178 to the controlV grid of triode in switch 13. This junction is also connected through a capacitor 180 to the control grid of a triode 181 of glow tube switch 19. The control grid of triode 181 is connected to ground through both a resistor 182 and a normally open switch 184. Switch 184 is mechanically connected to switch 177 so that switch 177 is opened when switch 184 is closed. These two switches are referred to hereinafter as the reset switches. The cathode of triode 181 is connected to the cathode of a triode 186 and to ground through a resistor 187 which is shunted by a capacitor 188. The anode of triode 181 is connected to a positive potential terminal 190 through resistors 191 and 192.V The junction between these resistors is connected to ground through a capacitor 193. The anode of triode 186 is connected to terminal 190 through resistors 194 and 192. The tenth cathode of tube 17 is connected through a capacitor to the control grid of triode 186. The control grid of triode 186 is connected to ground through a resistor 196. The control grid of triode 186 is connected through a resistor 201 which is shunted by a capacitor 202 to the anode of triode 181, which is connected to the rst terminal of a resistor `203. The second terminal of resistor 203` is connected to the anode of glow transfer tube 17. The control `grid of triode 181 is connected through a resistor 198 which is shunted 4by a capacitor 199 to the anode of triode 186, which is `shunted -byt a rectifier 208. The cathode of Vtriode 206 is connected to groundV through a resistor 209 which is shunted by a capacitor 210. The `anode oftriode 206 is connected to a` positive potential terminal 211 through Yresistors 212 and 2-13. The junction between these resistors is `connected to" ground through a capacitor 214. The anode of triode 206 isv also `connectedrthrough a capacitor Y216 and a resistor 217 to the control grid 4of .a triode 218. A p The junction `between capacitor.` 216 and l `resistor w217 is connected to 4ground through a rectifier 219. YThe control gridof triode `2.18 is connected to 'ground through a resistorf22'0.` .The cathode of `triode 218k connected -tosground `through a resistor 221 which '5 is shunted by a 'capacitor 222. -The anode of triode 218 is connected to terminal-211 through resistor 224 and 213.

The anode of triode 218 is connected through a capacitor 226 to the control grid of a triode 227 of monostable multivibrator 21. The control grid of triode 227 isv connected to a positive potential terminal 228 through resistors 229 and 230. The junction between these resistors is connected to ground through a capacitor 231. The control grid of triode 227 -is connected through a capacitor 232 to the anode of a triode 234. The anode of triode 227 is connected to terminal 228 through resistors 235 and 230. The cathodes of triodes 227 and 234 are connected to one another and to ground throughY a resistor 236 which is shunted by a capacitor 237. The anode of triode 234 is connected to terminal 228 through resistors 238 and 230. The anode of triode 227 is connected through a capacitor 240` to the first cathode of glow transfer tube 18. 'The anode of triode Y 227 is also connected through a resistor 241 tothe control grid of triode 234. Thecontrol grid of triode 234 is connected AVto ground through a resistor 242.

The apparatus thus far described is actuated by switch 33 being opened momentarily. When the apparatus is utilized to control the gain of a seismic amplifier this 'switch can be opened at the time the explosive charge is'detonated. The opening of switch 33 results in a positive pulse being applied to the controlV grid of triode ,40. This pulse is amplified by triodes 40 and 49 and applied to the control grid of thyratron 63. The output pulse from thyratron 63 is of an amplitude and shape which is independent of the starting pulse. AIf desired, a starting pulse can be obtained by momentarily closing switch 60. This results in a'negative pulse being applied to then-control grid of triode 49. Switch 38 should be closed at this time to prevent extraneous pulses being applied toftriode 40 from switch 33. The thyratron anode circuit preferably is adjusted sothat the thyratron Aremains inoperative for yseveral seconds after liring'and then automatically resets. This prevents spurious pulses in the input circuit from causing erratic operation.

The output pulse from thyratron 63 is applied to switch 13 which is a bistable multivibrator. This multivibrator controls the anode voltage of triode 94 of pulse generator .-14; The multivibrator isY flipped on by the output pulseffrom thyratron 63 so thatpulse generator 14 commences to oscillate. The frequency VofV oscillations of lgeneratory 14 is determined bythe resistance in the cathode circuit of triode 94. This-oscillator is of Vsubstantially the form described in Time Bases, Puckle,

John Wiley,` New York, pages 37-41 (1951)., Switch 1,3 can. beturned ofZ by the reset switch 184- in the ymanner described hereinafter. 1 f.

-The `output pulses from generator '14Kare'applied to .pulseshaper` circuit 15. Each positive input pulse applied to shaper v15` results inY a Vpair lof output pulses being to thevguide electrodesof tubes.1r7v'and 18.

It can be seen that the tw'o glow'transfer tubes are connected'in parallel, with respect to the guide electrodes,

so'xthat the glows tend to move'synchronously around each tube. vHowever, switch -19 controls `the-anode voltage; on the two glow tubes so that only one tube to'the lirs't lcathode ofitube 17'fso that: the discharge isibetween'y thelirs'Lcathode ofvtube 17 andthe A"anode -i-thereof. The output. pulses froms'haper'lS 'result' in '-1 the discharge transferring to successive'cathode'.s.y When if the glow leavesthe tenth cathodey afnegative'plsfeis l "applied to fthe control-gridbfftode.186. This resultsy in'switch 19 being'ipped so that a positive bias potential is applied to the anode of tube 18. g

The arrival of the discharge at the tenth cathode of tube 17 results in a positive pulse being tpplied to the input of delay amplifier 20. The output pulse from the delay amplier triggers monostable multivibrator 21. The output of this circuit is dierentiated by capacitor 240 to form a large negative pulse which is applied to the rst cathode of glow transfer tube 18. In order to reduce the time required for glow transfer tube 18 to become energized after -the pulse generator switch is triggered, a light 245 is directed on the tube.

Thus, at the beginning of the operation the glow is on the first cathode of tuber17 and remains at this position for an Vindefinite period. An input pulse to the system results in this glow transferring along the cathodes of the two tubes at time intervals determined Vby the frequency of pulse generator 14. When the glow leaves the next to the last cathode of tube 18 a negative pulse is applied directly to the controlgrid of triode 80 which turns otf switch 13. The glow thus stopson. the last cathode of tube 18 and remains at this position.

The sequential amplitude values of the desired output signalr are established by the settings of the contactors of potentiometers 141-150 and 161-170. The contactors of these potentiometers are connected to re- Vspective, output'terminals 141b, 141b 158e and 161:1,

162a 17th:. These terminals are connected through respective isolating resistors 141b, 14217 150b and 161b, 162b, .'170b to the control grid of a pentode 250 of isolation amplifier 22 which is illustrated in detail in Figure 3.V The control grid of pentode 250 is connected to ground through a resistor 251. The cathode and suppressor grid of pentode 250 are Vconnected to ground through `a resistor 252.` The screen grid of pentode 250 is connected to a positive potential terminal 253 through a resistor 254. "The'screen grid of pentode 250 is connected to the cathode thereof through a resistor 255. The anode of pentode 250 is connected to a positive potential terminal 256 through a resistor 257. The anode of pentode 250 is also connected through a resistor 258 to one end terminal of -a potentiometer 259. The second end'terminal of potentiometer 259 is connected to a negative potential terminal Y260 throughV a resistor 261. The contacter of potentiometer 259 is connected to the control grid of a triode 263. The anode of triode 263 is connected to terminal256, and the cathode of triode 263 is connected to terminal 260 through aresistor 264. Parallel connected feedback resistors are Vconnected between the cathode of triode 263 and the .control grid Yof pentode'250.` The cathode of triode 263 is connected to a rst output terminal 265 and to Vthe Ycontrol gridof a triode 266 which forms a part of interpolation lilter 23.

The control grid of triode 266 isconnected to ground through a resistor 268.V The anode of triode' 266 is connected to a. positive potential terminal V270. The

`cathode of triode 266 is connected to a negativefpotential terminal 2271 through a resistor 272 and to a second negativeV potential terminal 273 through resistors 274 and The'junctionV between resistors 274 and275 is connected through aresistor 276 to 'the control grid of a triode 277.1 The controlv grid of triode 277 is connected to ground through a capacitor 278. The anode of triode 277 is connected to terminal V 270. "The cathode of triode 27 7 is connected ,to terminal 271,.,through a resistor 280 and to terminal 273through Aresistors 281 and 282. The

".junction between resistors *281 land v 282 4is connected Athroughal resistor 283 and an iuductori 284 to the control `gridof a 'triode`285. The control grid of ltriode 285 is connected to groundthrough a capacitor 286. The

anode of triode 285 'is connected'to terminal .270.. The

.cathode of .t'riode'i285` is`connected to terminal 271 'through a resistor :290. The cathode of triode'285is also'connected-toterminal 273 through resistors 291 and .292. A variable resistor 293 is` connected .in parallel withk agences cathodes.L In theiillustrated embodiment threev potenti-A *l i ometers are connected to each of the cathodes. Correl f vresistor A292.' AThe ljunctionl between. resistors 291 and 293. is. connectedk throughra resistor 294 andv an inductor 295 to the control' grid of a triodezil't. `A capacitorr297 y v is connected'betwcenthecontrol grid of rtriode 296 and` groundi The anode of triode 296 is 'connected to-aposi-r I I tive potential terminal 270. The cathode of triode296 is f connected to. terminal 271 .through a resistor 298.

- The cathodeof triode 296 is also'connected tothe first:

end terminal of a potentiometer 300. The' second end vterminal of .this potentiometer is connected to ground.

- The contacter of potentiometer 300 is connected toi the l l control grid of a triode 301 of output amplierf24. The

`'tube 18. The 'last cathode of tube 17-"supplies ia-pulse f which is .applied through ka transfer amplifier 325 tok anode ofy triode3il1'is connected to a positive potential terminal 302.

knectedto a negative potentialterminal `303 through a v of ktriode 365 is connected yto ground. i iThe anodel of l directly vtothecathode of .triode 305. The kcontrol kgrid l=triode is connected toterminal 302. through a relsistou: 336'. 'Ifhel anode of triode 306 is also connected to a. negative potential .terminal 3081 through `resistors 369 and 310, 'a potentiometer` 311 and resistors 312 and 3,13.. vThe contactor of potentiometer 31.1`is connected io the control grid 'of ya triode 315.A t The anodeof'triode l 315 is connected to terminal 302. The cathode Vof ytriode i 3.15 isl connectcdto terminal 308 through a resistor 316.

The cathode of triode 315 i'salso connected toan output `terminal 317. Thesecond output terminal 318 is con i nected to ground.

The isolating resistors i 114112, .1426V 150k.r and 16111, 162b .170b are-employed to. make the adjustments of the potentiometers in the cathode circuits establishedV on potentiometers.

of the glow transfer tubes independenti of ione another. l f

. i lsponding lfirst potentiometers in each of these groups are connected through afiirst gate circuit 319y Ato ytlieinput vi l of isolationv amplifier 22", Corresponding second ipo` ltentiometers yin each of the groups are connected through asecond gate circuit 320 yto the'input ofl lamplifier 22'.y

Corresponding third potentiometers in each of ythe groups arezconnected through a third gate circuit 320 tok the in-` These three gate circuits .are ac-l tuated by respective driver circuits 322, 323 and 324' `put of amplifier 22.

which .in turn are controlled by a second glow transfer actuate a second pulse shaper 32.6.` The output pulses from Shaper 326v control thedischarge. transfer along they cathodes ofY ktube 18'.k `The third cathode lof tube 18 '329 and'3'30 connected in series between a positive lpo .tentialterminall-andground A normally closed re' set switch 332 is connectedk in parallel with resistor 330.

'A' rcapacitor `333 connected. -between .ground and the n K junction between resistors 328v and 329. The junction r:between resistors 329 aud`330 connected through `a` first ycapacitor 33410 an: 'outputzterminal 32S which is connected to thecontrol grid of triode 80 (see' Figure 2') in pulse `generator switch 13. The junction between re#l f lsistors 329 and 330 is also connected through-a capacitor Tbevoltages appearing at `the contactors of each of the i f ptentiometers are combined and amplified by amplifier 22. The vstepped output voltage-from amplifier 22 gener-l ally must besmoothed before iti can be used to control the gain ofthe seismic amplifier. If such a smoothing is signalcan betaken between terminal 265`and ground.' The smoothing of kthe stepped output functionr is kbasedk upon a convolution of a rectangular step with an isosceles triangle. This convolution is performed by passing the stepped function through a lter having approximately a triangular impulse response. The illustrated lter comprises one RC network andrtwo RCL networks. The individual networks are separated by cathode followers to make their parameters independent of each other. Considerable attenuation occurs in the interpolation filter so that the output'amplilier 24 is employedto provide a signal capable of controlling the gain ofaseismic amplifier, such as 25. i A

One of the main advantages of the function generator thus far described is the ease by which-a function can be A voltmeter can be placed across output terminals 317 'and 318; Y Potentirst step of the signalV is obtained. Switch 134 is then 33S; `to therst cathode of` tube 17'.

`ometers 341a, 341b and 341c-.areconnected in parallelk relationship with one anothervbetween the first cathode of tube 17' andground. Corresponding potentiometers are connected between each of the othernine cathodes andl lground.l lGuide :electrodes 124 and -125' are ac` tuated by the output pulses of; pulse Shaper 15.y i vThe f Threee potenti anode of `tube* 17' is connected to a positive potential yterrniualzfSS. through resistors` 356 and r357. The june# i .tion between these resistors is connected to ground 1 l i through a capacitor 358.

The tenth cathode of tube 17 is connected through a capacitor 360 to the control grid of a triode 361 which forms transfer amplifier 325. The control grid of triode 361 is connected to ground through a resistor 362. The `cathode of triode 361 is connected to ground through a resistor363. The anode of triode 361 is connected to a `positive potential terminal 364 through resistors 365 and 366. The junction between these resistors is connected to `ground through a -capacitor 367. f f

The anode of triode 361 is connected through a capacitor 370 to the. control gridof a triode 107 of pulse Shaper 326. The circuit of pulse Shaper 326 is identical to that of pulse 4Shaper 15, illustrated in Figure 2, and

v corresponding elements `are`designated by like primed refclosed to apply a positive pulse to pulse Shaper 15. This transfers thedischarge'to Ithe second' cathode olhibe`17.`-

Potentiometer 142 is then adjusted until the output signal represents the `desired fseco'ndstep ofthe signal. This procdure is continued to set ther-remaining "potentiometers.

In Figure 4 thereis shownya second embodiment of the function generator which lis adapted to provide a signal having'rajarge number of selected values.:y The input pulse shaping portionof this-function g'eneratoris identical to that illustrated in Figures 1 and 2 andcorresponding elements are designated-by like primed reference numerals. The Aoutput pulses" from `pulse shaper 15' are applied toV a rstfunctioniglow tran'sfe tube 17' which orrespondsto'tube 17 of Figure'l. i The output 'circuit of tube 17' diifersfromthat 4of, tube '17 in that a plurality of potentiometer-s is connected to eachof the,

`erence numerals. t The two output terminals vof pulse Shaper circuit 326 'are connected tothe guideelectrodes 151' and 152 of tube 18'. i'

`The illustrated embodiment of the function generator of Figure 5 provides a\ signal `having thirty set amplitude values. In this embodiment only the first three cathodes `of tube'18' are needed.` Resistors 372, 373 and`374 are connected between these respective cathodes and ground. The anode of tube 18 `is connected toa positive potential terminal 375 through resistors 376 `and377. Q'Ihe junction between these` resistors is connected to `ground through a capacitor 378." f

The `contactors of corresponding rst potentiometers in each group yof.pc tentio'meters connected to the `cathodes of tube 17 are `connected to respective first terminals of `isolating resistors 341:1', 1342a' 2:50a'.r The second '.terninals of lthese resistors are connected to one another A.and f to the contactor Vof a potentiometer 380e in gate circuit 3191. 'Iheirst iendterminal of `potentiometer 380e:

...tuur

Vtube 17' tires initially so I. cathodes of tube 17.

to open Gate No. 3. The transfer -is connected through a rectifier 3`8la and a resistor 382e aas-H338 to a positive potential terminal 383:1. The secondfend terminal of potentiometer 380:1 is connected through a rectifier 384:1 and a resstor'385a to a negative potential terminal 386:1. The junction between rectifier 381a and resistor 382:1 is connected to'the junction between rectifier 384:1 and resistor 385:1 through series connected rectiers 388:1 and 389:1. The junction between these last two rectiers is connected through a'rectiiier 390:1 to an output terminal 391. y A

The first cathode of glow .transfertube 18 is connected through a resistor 400:1 to the control grid of a triode 401:1 in driver circuit 322. The control grid of triodey 401:1 is connected to ground through a` resistor j 402:1.` The cathode of triode 401:1 is connected to a negative potential terminall 403:1 througharesistor 404a. The cathode of triode 401:1 isalso connectedthrough a rectifier 405:1 to the junction between rectiiiers 381:1 and 388:1. The anode of triode 401:1 is connected to a positive potential terminal 405:1 through a resistor 406a. The anode of triode 401:1 is also connected through a resistor 407:1 to the control grid of a triode 408:1. The control grid of triode 408a is connected to a negative potential terminal 409:1 through a resistor 413:1. The anode of triode 408a is connected to terminal 405a, and the cathode of triode 408:1 is connected to terminal 403:1 through a resistor 410:1. The cathode of triode 408:1 is also connected through a rectifier 411:1 to the junction between rectifers 384:1 and 389:1. The first cathode of -tube 18 is also connected through/a capacitor 412 to the junction between resistors 329 and 330 of the reset circuit.

Output terminal 391 is connected to the control grid of pentode 250 in isolation amplifier 22' ofthe form illustrated in Figure 3.

The corresponding second and third potentiometers which are connected to each of the cathodes of tube 17 are connected through corresponding isolating resistors to respective gate circuits 320 and 321. These circuits and their corresponding driver circuits are identical to the circuits thus far described. The gate circuits are of the type described by Millman and Puckett in Proc. I.R.E., 43, 29-37 (1955).

When the glow discharges leaves the third cathode of tube 18', a pulse is applied through a capacitor 420 to the control rgrid of a triode 421 of amplifier 327. The cathode of'triode 421 is grounded through a resistor V423, and the anode of triode 421 is connected to terminal 364. The cathode of triode 421 is connected through 'a capacitor 424 to a terminal 425 which is connected to the control grid of triode 80 in the pulse generator switch, see Figure 2. This turns the pulse generator olf sequential desired output signals are set on 341:1', 350:1', 341b', Tube 18 tires at the same time that Gate No. 1 remains open the ten cathodes of tube as the discharge transfers down 17@ vWhen the discharge reaches the'tenth cathode of tube 17' a pulse is applied to theV` guide electrodes of tube 18through pulse shaper 326. vThis transfers the glow to the second cathode of tube 18 vto open Gate No. 2. V. The glow repeatsfthetransfer down the .ten At the end of the ksecond transfer the discharge in vtube 18l moves to the third cathode A again repeats in tube VThe function generator shown in Figures 4 and 5 pro-v i videsvthirty selected output voltages. It should beevident that-this can readily be extended -to one hundred points there is provided vau limproved signal generator which is yit) particularly useful to control the gain 'of' a seismicfamplidier. Any arbitrary electrical signal can be generated by setting sequential values fon theV potentiometers. While the invention has been described in conjunction with the present preferred embodiment, it'should be evident that it is not limited thereto.

1. Electrical signal generating apparatus comprising va glow transfer tube having an anode, a plurality of cathodes, and guide electrode means; a plurality of potential dividing networks connected between each of said cathodes and a reference potential; meanstoapply a potential to the anode of said tube which is positive with-respect to` said reference potential; means to apply pulsesat a predetermined rate to said guide means to transfer'a discharge between adjacent cathodes and 'saidanode; a-pluirality of gate circuits each 4 having'an output terminal; outsaid networks; means to apply the picked off potentials of corresponding networks connected to each of said cathodes to a respective one of said gate circuits; and means to open adjacent ones of said gate circuits at time intervals corresponding to the time the discharge moves past output of said first iilter,

all the cathodes in said tube.

2. The combination in accordance with claim 1 where-V in said last-mentioned means comprises a second glow transfer tube having an anode, a plurality of cathodes, and guide electrode means; means to apply a potential to the anode of said second tube which is more positive than said reference potential; means responsive to a discharge being at a selected cathode of said first-mentioned tube to generate a second pulse; means to apply said second pulse to the guide means of said second tube; and means to open a corresponding gate circuit responsive to a discharge at respective ones of the cathodes ofsaid second tube.

3. The combination in accordance with claim 1 further comprising filter means to smooth the output signal provided by said means for generating voltages.

4. The apparatus in accordance with claim 3 wherein Said filter means comprises a rst cathode follower, a resistance-capacitance filter having the input thereof connected to the output of said first cathode follower, a second cathode follower having the input thereof connected to the output of said filter, aiirst resistance-inductance-capacitance iilter having the input thereof connected to the output of said second cathode follower, a third cathode follower having the input thereof connected to the a second resistance-inductancecapacitance filter having the input thereof connected to theoutput of said third cathode follower, and a fourth cathode follower having the input thereof connected to the output of said second filter.

5. `Apparatus for generating an mined manner comprising a glow transfer tube having means to transfer a discharge between adjacent cathodes and said anode, a plurality of potentiometers; means connecting the end terminals of each of said potentiometers to a respective one of said cathodes and to a reference potential, respectively; and means connecting the contactors of said `potentiometers in` determined by 6. The apparatus ofL claim 5 furtherV comprising Va s eis-` mometer, a'seismicamplifierv having; the vinput thereofelectrical signal which varies in amplitude with respectto timein a predeteran output V circuit so l that the sequential potentials-in the output circuit areff the settings of the contactors of the in-l dividual potentiometers as the discharge is transferred to l Y lthe associatedcathodes.

explosive charge and generate a first electrical pulse, means responsive to said first'electrical pulse to initiate a discharge between the first cathode of said tube and said anode, `and means connecting said output circuit to said seismic amplifier to control the gain thereof.

7. The apparatus of claim 5 further comprising a second glow transfer tube having an ;anode,a plurality of catbodes, and guide electrode means to` transfer a dischargebetweenadjacent cathodes and Vsaid anode; a pluralityof second potentiometers; means connecting the end terminals of-each of said second potentiometers to a respective one of said cathodes of said second tube and to said reference potential, respectively; switching means to apply a potential which is positive with respect to said reference ,potential selectively to one of said anodes; means to apply pulses at a predetermined rate to the guide electrode means of said tubes; means to initiate a discharge between the first cathode of the first-mentioned tube and the anode thereof, said switching means apply- `Resumes cited in the me of this patent UNITED STATES PATENTS 2,265,538 Minton Dec. 9, 1941 2,696,572 Schmid Dec. 7, 1954 2,702,357 Townsend Feb. 15, 1955 2,794,966 1957 McCarty a June 4, 

